The tear gas was released by opposition party Levizja Vetvendosje, according to Avni Byty-i, deputy chief of staff to Speaker Kadri Veseli.
But members of the staunchly nationalist political party Vetevendosje argue that the border agreement shouldn't be signed because it cedes 30 square miles of Kosovo's land to Montenegro.
But opposition politicians have alleged that the agreement gives away 8,000 hectares of Kosovo's territory to Montenegro.
"The border demarcation between Kosovo and Montenegro is not a bilateral problem". Kosovo needs to ratify the deal, which was signed by Kosovo and Montenegro in August 2015, to get visa free travel to the European Union for its citizens.
Analysts estimate the party has used tear gas in parliament more than 15 times, always over the issue of border demarcation.
Kosovo's parliament needs a super-majority of two-thirds to pass the border agreement, and the tear gas stunt might actually encourage the country's lawmakers to get on board, Selimi said.
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Later, police went into parliament and forced out a small group of opposition lawmakers, who had refused to leave since the morning. In order for it to be approved, two-thirds of lawmakers must support it.
The opposition party, now divided in two groups because of internal frictions, has used tear gas and similar tactics to disrupt parliament over the past three years.
Prime Minister Ramush Haradinaj said before the start of the session they had the votes to pass the deal.
Greg Delawie, the USA ambassador to Kosovo, expressed the same view.